The present invention relates to a projection type projector apparatus using a reflection type liquid crystal panel, such as a so-called liquid crystal projector or projection type television using forward projection.
Liquid crystal projectors for business use have widely spread. Furthermore, as a substitute for a conventional image display apparatus of such a scheme that an image displayed on a cathode-ray tube is projected onto a screen, development of a projection type television using liquid crystal display elements has been conducted.
Liquid crystal panels are classified into transmission type crystal panels and reflection type crystal panels, according to their types. In the reflection type liquid crystal panels, a beam passes through a liquid crystal layer twice and consequently the thickness of the liquid crystal layer can be reduced by that amount as compared with the transmission type liquid crystal panels. As a result, the reflection type liquid crystal panels are excellent in fast response performance, and consequently they are suitable for dynamic picture display, i.e., application of projection type television.
On the other hand, in the transmission type liquid crystal panels, the so-called ON state and OFF state are generated by a shutter operation of the liquid crystal itself. In the case of the reflection type liquid crystal panels, both a beam in the ON state and a beam flux in the OFF state are reflected on the same optical path, and consequently a polarization beam splitter (hereafter abbreviated to PBS) for conducting beam separation on the basis of a difference in polarization state becomes an indispensable component.
The PBS action on a reflection type liquid crystal panel will now be described by using FIG. 12. In FIG. 12, reference numeral 1 denotes a PBS, 5 a cross prism for performing dichroic action, and 6 a reflection type liquid crystal panel. In FIG. 12, if light aligned with S-polarized light in an illumination optical system or only S-polarized light in the illumination optical system is input to the PBS 1, then the S-polarized light is reflected by a PBS plane of the PBS 1 and input to the cross prism 5. White light incident on the cross prism 5 is separated into three colors R, G and B by the dichroic action. The R, G and B colored beams are input to the reflection type liquid crystal panels 6 respectively corresponding to R, G and B. If each pixel is in the ON state in FIG. 12, then each of the beams input to the reflection type liquid crystal panels 6 respectively corresponding to R, G and B is converted in polarization state from S-polarized light to P-polarized light, and reflected. On the other hand, if each pixel is in the OFF state, then each beam is reflected while it is still S-polarized light. Beams of R, G and B input to the cross prism 5 again are subjected to color synthesis by the cross prism 5. As for beams incident on the PBS 1, each of beams in the ON state is a P-polarized beam and consequently it is transmitted through the PBS 1 this time, input to a projection lens (not illustrated), and projected. On the other hand, each of beams in the OFF state remains an S-polarized beam and consequently it is reflected by the PBS 1 again, and returned to its original light source side.